1. Technical Field
This disclosure relates to an ink-jet recording process, a recording apparatus, an ink-media (recording medium) set and a record using an ink containing, instead of a conventional pigment, a polymer emulsion containing polymer line particles having a water-insoluble or hardly-soluble colorant. More specifically, it relates to an ink-jet recording process, a recording apparatus, an ink-medium (recording medium) set and a record which can produce a high-quality image with good color tone, satisfactorily absorb ink, he satisfactorily fixed, produce an image with outstanding fastness such as water resistance and light resistance and implement ink jet recording excellent in storage stability and discharge stability without head clogging in printing.
2. Description of the Related Art
Ink-jet printers exhibit low noise and low running cost and have thereby been widely employed. Color printers that can print not only ink-jet-dedicated recording media but also plain paper are now placed on the market. However, these printers cannot significantly satisfy all the requirements typically in color reproducibility, durability, light resistance and drying property of images, bleed in characters (feathering), color boundary bleed (color bleed), printability on both sides of medium (two-side printability) and discharge stability. An ink to be used is selected according to precedential properties depending on the purpose. Particularly, printers that implement high-speed printing on plain paper cannot significantly satisfy all these requirements, and a variety of proposals have been made on inks and recording media, respectively. For example, Japanese Patent Application Laid-Open (JP-A) No. 09-157559 and No. 09-132740 each disclose the use of a pigment ink having higher light resistance than a dye ink. JP-A No. 55-5183 and No. 56-148585 each disclose a receiving layer comprising a porous inorganic pigment arranged on a substrate of a recording medium for the purpose of improving ink absorption.
A pigment ink is generally anionically dispersed. Noting this, a process of compounding a cationic component in the ink-receiving layer to thereby aggregate the ink has been proposed to fix an image according to the above system. In this connection, a large amount of a cationic component must be used to fix a dye in a dye ink. In contrast, a pigment ink will excessively aggregate and distribute unevenly on the surface, thus leading to a decreased recording density, when such a cationic component is used in excess. The pigment ink thereby often fails to produce an excellent record on conventional recording media for dye inks. A pigment has a much higher molecular weight than a dye and requires an image-fixing mechanism such as control of bleed apparently different from that of a dye having a low molecular weight. In ink-jet recording process using a pigment ink, a droplet of the ink is discharged to a receiving layer to form an image, as in a dye ink. In such an ink-jet recording system, print quality is largely affected by the difference in ink absorptivity. Upon recording using a dye ink, the ink absorptivity increases but the print density significantly decreases with an increasing amount of the dye ink for forming a surface layer on a recording paper, since the pigment component is absorbed into the inside of the recording medium. In contrast, when the amount of a pigment ink is decreased to allow the pigment component to remain on the surface, bleed becomes worse, the ink solvent is not sufficiently absorbed by the receiving layer and the pigment particles move with the solvent. Thus, the pigment particles distribute unevenly on the receiving layer surface, a white background of the receiving layer is exposed from the printed portion and the print density often decreases. These two techniques require different properties on recording matters, and a variety of proposals have been made.
Referring to inks, inks for use in ink-jet recording generally mainly comprise water and further comprise a colorant and a wetting agent such as glycerol for preventing clogging. Dyes are used as the colorant for their excellent color development and stability. However, images produced by using such dye inks have insufficient light resistance and water resistance. The water resistance is improved to some extent by using improved ink-jet dedicated recording media having an ink-absorbing layer but is still insufficient on plain paper.
As a possible solution to these problems, pigment inks using a pigment such as an organic pigment or carbon black as the colorant instead of a dye have been developed. Such a pigment is insoluble in water and is used as an aqueous ink prepared by mixing and dispersing the pigment and a dispersing agent in water to thereby stably disperse the components in water. The use of a pigment can improve the water resistance and light resistance but does not satisfy all the other properties simultaneously, as in the above case. In particular, the pigment ink cannot significantly produce an image with high density and high color development when the ink is printed typically on plain paper at high speed, or does not sufficiently satisfy the requirements in character bleed, color boundary bleed and two-side printability.
In ink-jet recording, an ink must be stably discharged as droplets from fine nozzles of an ink-jet recording head and must not be dried and solidified in orifices of the ink-jet recording head. However, when the ink containing the dispersing agent is used in ink-jet recording, a resin or another component constituting the dispersing agent is loaded to the orifices and may not be dissolved again, thus leading to clogging or discharge failure of the ink. After a long downtime of printing, the nozzles and other parts may be often clogged and the ink with an increased viscosity deposits on maintenance mechanisms such as nozzle caps or suction tubes to thereby deteriorate the functions thereof. When printing is sustained temporarily or sustained in a nozzle corresponding to a blank in a document or image, the direction of the ink droplets ejection is disturbed and thereby print failures (failures in intermittent discharge) often occur.
An aqueous pigment ink containing a dispersing agent is generally viscous, thereby shows high resistance in a pathway to the tip of a nozzle and is discharged unstably, thus failing to produce a record smoothly.
For solving these problems, JP-A No. 2000-212486 discloses an ink and a set thereof, comprising a pigment, a water-soluble dispersing agent, a specific penetrating agent and polyhydric alcohol alkyl ether derivative, in which the types and concentrations of the pigment and the resin constituting the dispersing agent are specified in combination.
The ink disclosed herein is very highly penetrable, thereby can be dried sufficiently and discharged stably even in high-speed printing, but shows inferior image density and color reproducibility on plain paper to a dye ink. The character bleed, color boundary bleed and two-side printability are improved as compared with images formed by conventional ink-jet recording techniques but are inferior to images recorded typically by electrophotography generally used in the market in printing on plain paper.
As a possible solution to improve the image durability, an ink containing a colorant-including resin dispersion has been proposed. The dispersion comprises a water-insoluble but dispersible resin including a colorant. However, this ink does not produce an image with a sufficient density when carbon black is used as the colorant, and shows inferior image density and color reproducibility on plain paper to a dye ink when a color organic pigment is used as the colorant in a conventional ink formulation. In addition, an ink set comprising the colorant-including resin dispersions as the black ink and color inks shows some color boundary bleed between the black and yellow colors.
Self-dispersible pigment inks which can be dispersed stably without using a dispersing agent are known as another dispersing technique. As black pigment inks, “self-dispersible carbon blacks” capable of stably dispersing without using a dispersing agent have been developed, as disclosed in JP-A No. 05-186704, No. 08-3498 and No. 10-140064. These self-dispersing carbon blacks each have a hydrophilic group introduced to the surface of carbon. Color pigments for use in color pigment inks capable of stably dispersing without using a dispersing agent have been developed, as disclosed in JP-A No. 2000-513396. These color pigments are modified with a surface modifier containing an ionic group or ionizable group.
The combination use of these self-dispersible pigment inks, however, leads to a color image with low color saturation on recording media and low scratch resistance on glossy paper and other dedicated recording media. When a resin emulsion is added to improve the scratch resistance, the ink disperses less stably and is therefore discharged less stably.
Aforementioned JP-A No. 10-140064 also discloses an ink set of a black ink and color inks, in which the black ink contains a self-dispersible carbon black and each of the color inks contains a colorant having a polarity opposite to the colorant of the black ink.
JP-A No. 2000-191972 discloses an ink set having improved bleed resistance and comprising a self-dispersible carbon black ink and color inks each containing ions with polarity opposite to that of ions in the self-dispersible carbon black ink. Prints produced by using these ink sets show improved color boundary bleed but are still insufficient in other properties than the color boundary bleed.
Improvements of the printability of recording media have been also made on ink-jet dedicated recording media of coated paper type comprising a substrate and a coating layer arranged on the substrate.
For example, No. 57-82085 and No. 57-135190 each disclose ink-jet recording sheets which contain a plastic pigment and have been subjected to heating and calendering as in JP-A No. 06-79967. These publications describe that the ink-jet recording sheet using a plastic pigment has satisfactory ink absorptivity and gloss but shows decreased color reproducibility and color density and thus fails to produce sharp images, since the sheet must contain a large quantity of voids between particles of the plastic pigment for keeping its ink absorptivity and the plastic pigment thereby has a high refractive index. They also describe that, when the ink-jet recording sheet is subjected to calendering or super-calendering to impart gloss thereto, the voids in the coating layer decrease with an increasing gloss, thus inviting slow absorption of the ink and ink flood due to insufficient absorptivity, and that the sheet absorbs ink more slowly in a less amount than an ink-absorbing layer comprising pigment fine particles such as silica.
As an ink receiving layer that rapidly absorbs inks without bleeding, these publications describe a layer comprising a binder and an inorganic pigment such as silica particles or alumina particles dispersed in the binder. An ink-jet recording material having this layer as the ink-receiving layer is referred to as a void-absorption or pore-absorption type recording material. In this material, the ink enters the voids among the inorganic pigment particles occupying about 90% of the layer to produce a print. The layer of the silica particles or alumina particles is often white or opaque white as a background.
Examples of ink-jet recording media having an ink-receiving layer mainly comprising a water-soluble resin can be found in JP-A No. 11-342669 as an ink-jet recording medium containing hydroxypropyl methylcellulose and having an ink-receiving layer containing a homopolymer of N-vinylpyrrolidone or a copolymer of N-vinylpyrrolidone and another polymerizable monomer; JP-A No. 2000-108508 as an ink-jet recording sheet comprising a methoxy-containing water-soluble cellulose derivative and water-soluble cationic resin; and JP-A No. 10-329405 as an ink-jet recording sheet containing a hydrophilic polymer resin and a specific anionic fluorine-containing surfactant.
Certain ink-jet recording sheets having an ink-receiving layer mainly comprising an inorganic pigment and binder can be found in JP-A No. 10-119417 as an ink-jet recording sheet comprising a substrate sheet, an ink-permeating layer mainly comprising an inorganic filler and an ink-swelling layer mainly comprising a water-soluble resin, both arranged on the substrate sheet; and JP-A No. 10-329417 as an ink-jet recording film comprising (A) an ink-receiving layer containing a water-soluble resin, a surface-roughening agent and a crosslinking agent, and (B) a layer containing a dot shape controlling agent, in which at least two synthetic silica having different oil absorption are used as the surface-roughening agent, and the amounts of these surface-roughening agents are controlled to thereby set the number of standard wiping of the recording layer at 20 to 100 and the ink-fixing time at 5 minutes or less.
JP-A No. 11-99739 describes an ink-jet recording sheet having a first ink-receiving layer and a second ink-receiving layer arranged on the first ink-receiving layer, in which the first ink-receiving layer serves to receive and absorb an ink which the second ink-receiving layer does not completely absorb, and contains a resin component which is dissolved in or swelled by the coating composition for the second ink-receiving layer, and the content of the pigment in the second ink-receiving layer is larger than that of the first ink-receiving layer.
JP-A No. 11-245502 describes an ink-jet coating agent containing 15% by weight to 90% by weight of a water-absorbing polyurethane and, in addition, 10% by weight to 80% by weight of a silica mixture on the basis of solid content of the total coating agent, in which the silica mixture comprises 10% by weight to 30% by weight of a silica having an average particle diameter of 6 to 9 μm, 15% by weight to 40% by weight of a light scattering silica having an average particle diameter of 10 to 15 μm, and 15% by weight to 40% by weight of a porous silica having an average particle diameter of 10 to 22 μm. JP-A No. 11-291619 describes an ink-jet recording film having an adhesive layer and an ink-receiving layer sequentially arranged, in which the adhesive layer mainly contains (A) a binder, (B) a film-forming auxiliary and (C) a crosslinking agent, and the ink-receiving layer mainly contains the same binder as the component (A), (D) surface roughening agent, the same crosslinking agent as the component (C), and (E) a catalyst, wherein the weight ratio of the binder to the surface-roughening agent in the ink-receiving layer is from 2:3 to 1:3.
JP-A No. 11-301093 describes an ink-jet recording material having an ink-receiving layer and an ink-solvent-permeating layer arranged on the ink-receiving layer, which ink-solvent-permeating layer allows a solvent to pass therethrough but does not allow a pigment to pass therethrough. JP-A No. 2000-1043 describes a recording material for aqueous ink, formed from a resin composition comprising a polyvinyl acetal resin, a urea-glyoxal-acrylamide polycondensate and/or an epoxy compound, and fine particles. JP-A No. 2000-79752 describes an ink-jet recording medium containing typically a synthetic silica and a cationic resin having a cationic intensity of 1.5 mEq/g or more and 6 mEq/g or less. JP-A No. 2000-79752 and No. 2000-79754 each describe a partially erasable recording sheet having an ink-receiving layer bearing an ink-jet printing pattern formed by a pigment ink which is incompatible with the ink-receiving layer.
JP-A No. 2000-127610 describes an ink-jet recording sheet comprising porous starch particles and a binder resin, which porous starch particles contain inorganic or organic fine particles embedded in their pores. JP-A No. 2000-141876 describes an ink-jet recording sheet mainly comprising a polyvinyl acetal resin and containing a polyvinylpyrrolidone resin, a urea-glyoxal-acrylamide polycondensate and/or epoxy compound, and fine particles. JP-A No. 2000-190622 describes an ink-jet recording material having an ink-receiving layer containing an inorganic pigment, a water-insoluble resin and a metal salt having an ion valency of 2 or more. JP-A No. 2000-238420 describes an ink-jet recording sheet having a recording layer, in which the recording layer mainly contains a synthetic silica having an average particle diameter of 3 to 15 μm as a pigment and a poly(vinyl alcohol) having a degree of saponification of 96% by mole or more as a binder, wherein the binder is contained in an amount of 10 to 50 parts by weight to 100 parts by weight of the pigment, and the recording layer further contains 1 to 40 parts by weight of a quaternary ammonium salt polymer to 100 parts by weight of the pigment, and 20 to 100 parts by weight of a curing agent to 100 parts by weight of the binder.
JP-A No. 2000-247014 describes a recording material for aqueous ink, which mainly comprises a polyvinyl acetal resin prepared by treating a poly(vinyl alcohol) with an aromatic aldehyde into an acetal and further comprises a water-soluble acrylic resin, a water-soluble epoxy compound and fine particles of at least one selected from silicic acid, silica, kaolin, clay, alumina, calcium carbonate, zeolite, titanium oxide, talc and spherical polymers. JP-A No. 2000-318298 describes an ink-jet recording sheet having a smoothness of 5 sec or more and 40 sec or less and comprising a resin film, a lower layer containing an amorphous synthetic silica and a water-insoluble resin, and an upper layer containing an amorphous synthetic silica, a water-insoluble resin and a silanol-modified poly(vinyl alcohol).
Regarding an aluminum oxide-containing receiving layer, JP-A No. 06-79967 describes an ink-jet recording sheet comprising a substrate and an ink-receiving layer having one or more layers of an alumina hydrate, in which the ink-receiving layer and the image recorded region after receiving the ink have a 60-degree specular gloss of 25% or more and 20% or more, respectively. The alumina hydrate is a high-molecular-weight alumina generally called as an alumina sol, has satisfactory ink permeability, has a high positive charge and is therefore suitable as image-fixing of a dye in the ink. The alumina sol herein comprises particles preferably in the form of pseudoboehmite and boehmite and more preferably in the form of fiber. However, JP-A No. 11-198520 mentions that an ink-jet recording material using such a boehmite alumina sol has very high surface gloss but has a low pore volume, thereby absorbs less amount of the ink and must be formed as a thick layer, as described typically in JP-A No. 05-24335. As is described above, preferred requirements of recording media vary depending on the types of ink and/or recording conditions and are not always constant.
JP-A No. 2000-37945 describes an ink-jet recording sheet having an ink-receiving layer comprising two types of aluminum oxide fine particles bound by action of a binder, in which the two aluminum oxide fine particles have different particle diameters, and the mainly contains a partially saponified poly(vinyl alcohol) having a degree of polymerization of 1000 or more and a degree of saponification of 80% by mole to 95% by mole. Aforementioned JP-A No. 11-198520 describes an ink-jet recording material as a laminate of a layer of γ or δ aluminum oxide and another layer containing a water-soluble or water-swellable polymer. These recording sheets, however, do not satisfy ink-jet suitability such as ink absorptivity, image density, beading and image-fixing properties (scratch resistance) in ink-jet recording using an “ink containing a polymer emulsion comprising polymer fine particles having a water-insoluble or hardly-soluble colorant” which resembles to but is distinguished from conventional regular pigment inks.
Certain media for use in ink-jet recording are known, which comprise a substrate such as plain paper or an ink-jet-dedicated coated paper, and an ink-receiving layer arranged on the substrate and comprising a pigment such as amorphous silica and a water-soluble binder such as a poly(vinyl alcohol). As the substrate for such media, paper is conventionally used, and the paper substrate plays a role as a layer for absorbing the ink solvent. With an increasing demand on image quality similar to that of silver halide photographs and an increasing demand to provide glossy texture of the surface of media, a non-absorbable resin-coated paper similar to silver halide photographic paper is used as the substrate. The ink absorptivity and surface smoothness of an ink-receiving layer therefore become important. Improvements have been made to incorporate a silica prepared by the gas phase process or alumina fine particles into an ink-receiving layer to thereby increase the surface smoothness and porosity of the ink-receiving layer.
For example, JP-A No. 06-79967 discloses a cast glossy paper having an ink-receiving layer containing an alumina hydrate as the outermost layer. However, this paper shows a large amount of cracking on the outermost layer and invites the ink to bleed in printing or the substrate to absorb the solvent in the ink, leading to curling and cockling. JP-A No. 2000-351267 discloses a recording medium and process having satisfactory absorptivity for a pigment ink and good image-fixing properties for the purpose of increasing not only initial image quality but also image fastness to those of silver halide photographs. However, when this technique is applied to a pigment ink containing no polymer in a dispersing agent, such as a self-dispersible pigment or surfactant-dispersing pigment, it invites a lower gloss of images than the surface of the medium or insufficient image-fixing properties such as scratch resistance. Further improvements have therefore been demanded.